Power-over-Ethernet (PoE) is a standard to supply power to detached data equipment and peripherals (like routers, switches, printer spoolers etc.) through the same wire or network connection that is already used to connect these to the Ethernet. Currently, discussions are coming up to make use of the same standard for all kinds of low power loads such as, e.g., lighting equipment (sensors, switches, light sources etc.) or entertainment appliances like active speakers, internet radios, DVD player, set-top boxes and even TV sets. Here, actual standardization in IEEE802.3 is going on to support power levels even up to 100 W per Cat5/6 connection.
One upcoming field for applying PoE is in lighting systems. The new generation of LED based lamps makes use of a central power supply as provided by PoE in the network infrastructure. In addition, the use of cheap network cables reduces installation costs and inherent safety (due to low DC power) and polarity independence reduces installation errors which, if they occur during installation, can be identified immediately, because power does not need to be shut off as in conventional lighting installations directly connected to mains. Typically, load devices are light sources. However, other devices like sensors or user interface devices (switches, control panels) may also be powered by PoE.
As PoE supply systems for power distribution inside of buildings get into the view of the industry, some specific usage aspects of these networks need to find solutions in order to get these direct current powered networks (so called “DC-Grids”) widely employed. When the PoE standard was introduced for supplying power to detached networking devices like routers, switches, printer spoolers, etc., it was a replacement for small power-plug type power supplies, since the originally intended loads where mostly already equipped with communication and processing means.
FIG. 1A shows a typical connection of a conventional PoE system comprising a power sourcing equipment (PSE) 1 and one PoE load 20 usually called a powered device (PD). A connection may be implemented by means of a so called patch cable 14 between one of a plurality of output jacks or ports 12, 13 of the PSE 1 and an input jack or port 21 of the PD 20. In PoE systems, typically power supplies 11, 24 and data connectivity of data processing functions 19, 25 are sharing the same patch cable 14. In multi-load systems, each load is connected to a separate one of the plurality of output ports consisting of first port (P1) 12 to n-th port (Pn) 13 of PSE 1, while PSE manager 18 takes care of the correct powering. So each load, such as PD 2, indicates separately the suitability for receiving power over the Ethernet connection and negotiates separately the availability of required power with PSE 1. This requires a powered device controller 23 in each load (i.e. PD 20). On the PSE side, PSE management controller 18 supervises the negotiations on all ports.
However, in the new application field of lighting systems or similar load systems with often small loads with low local computing and communication requirements, sometimes the overhead of communication and processing compared to the load complexity is inappropriate. Moreover, another shortcoming of PoE is its purely star-based network topology, while lighting systems are often wired in a serial manner (i.e. daisy-chained). Due to this, implementation of the star-based PoE in these kinds of typically serially connected load systems would lead to increased total cable lengths and thick cable bundles in comparison with a truly serially connected implementation.
A conventional PoE lighting system 100 with a PoE switch 110 (being supplied via mains connection 111) and a number of luminaires 132, 133, 134, 135 connected thereto by means of Ethernet connections 121, . . . , 125 is shown in FIG. 1B. A typical luminaire 132, 133, 134, 135 in a conventional PoE lighting system 100 comprises lighting modules (such as, e.g., LEDs) generating light and an electronic section, controlling the LED current. The luminaire further comprises an interface (exemplary indicated by reference sign 135a for luminaire 135) to the PoE connection for negotiation and voltage adaptation.
US 2006/100799 A1 discloses a method and apparatus for managing an Inline Power relationship between and among a first network device acting as power sourcing equipment to provide Inline Power to a second Powered Device and a third device. In one aspect of the invention, the powered device(s) and the third device are powered (at least in part) by the PSE using inline power from at least one port (which may include more than one PSE) and they are powered over one or more sets of cables.